1. Field of the Invention
The present invention relates to a method for radiation beam welding a first member to a second member of an electromagnetic actuator, a body made using the method and a lithographic apparatus comprising such a body.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
Scanning of the wafer and/or reticle is usually performed by a stage system, for instance a stage system including two stages put on top of each other, wherein one stage is used for coarse positioning and the other stage is used for fine positioning. Current stage system designs use electromagnetic actuators in which an electric current carrier interacts with a magnetic field generated by permanent magnets. A disadvantage of these actuators is that the electric current running through the electric current carrier dissipates a lot of energy thereby increasing the temperature. The temperature increase has an influence on the surrounding parts thereby reducing the accuracy of the apparatus. Further, the maximum allowable temperature of the electric current carrier limits the allowable electric current and thus the force that can be applied by the actuator.
In order to keep the temperature of the actuators within predetermined limits, the actuators may be cooled using cooling bodies with cooling channels around the electric current carrier thereby removing the dissipated heat and acting as a thermal shielding towards other parts. The cooling bodies are formed by connecting two plates to each other, wherein in one of the two plates recesses or cavities are formed as channels, and the other plate is used to close off the channels. The two plates may be connected to each other by laser beam welding.
However, when using laser beam welding to connect the two plates together, the maximum load a welding seam can withstand is limited due to oscillating loads as a result of the actuators driving cycle and as a result of pressure loads in the cooling channels when pumping around cooling liquid.